Swash plate type variable displacement compressor

ABSTRACT

A swash plate type variable displacement compressor includes a crank chamber, a rotary shaft, a swash plate, a piston, a supply passage and first and second bleed passages. The supply passage connecting the crank chamber to a discharge pressure region is provided with a displacement control valve. The pressure in the crank chamber is varied by adjusting the opening of the displacement control valve. The first bleed passage connecting the crank chamber to the suction pressure region is provided with a valve. The second bleed passage constantly connecting the crank chamber to the suction pressure region is provided with a throttle. The valve operates to close the first bleed passage according to the magnitude of centrifugal force generated by the rotation of the rotary shaft.

BACKGROUND OF THE INVENTION

The present invention relates to a variable displacement compressor foruse in an automotive air conditioner, and the like.

Generally, a variable displacement compressor (hereinafter referred toas “compressor”) is known as a compressor for use in an automotive airconditioner that is operable to variably control its displacement. Thistype of compressor uses a displacement control valve for adjustingpressure in a crank chamber to change the inclination angle of a swashplate accommodated in the crank chamber, thereby to adjust the strokelength of pistons and hence to control the displacement of thecompressor.

Japanese Unexamined Patent Application Publication No. 10-54350discloses the compressor having a valve disposed in a bleed passageconnecting the crank chamber to a suction pressure region of thecompressor. The valve includes a valve body a coil spring and acounterweight. The coil spring urges the valve body in the directionthat causes the valve body to open a valve hole. When the rotationalspeed of the rotary shaft reaches a predetermined value, the valve bodyis moved in the direction that causes the valve body to close the valvehole by centrifugal force acting on the counterweight, which closes thebleed passage and stops the flow of refrigerant gas from the crankchamber into the suction region through the bleed passage. During thecompression operation under a large displacement, the valve closes thebleed passage and the pressure in the crank chamber is graduallyincreased by blow-by gas flowing into the crank chamber. Thus, thedisplacement of the compressor is decreased so that the compression loadis reduced and the contact pressure acting on various sliding surfacesof the compressor is reduced, accordingly.

However, according to the reference No. 10-54350, the bleed passage isclosed by the valve when the rotational speed of the rotary shaftreaches the predetermined value or more, with the result that the amountof refrigerant gas drawn from the crank chamber into the suctionpressure region becomes zero. In this operating state, it takes a longtime to increase the displacement of the compressor, and thedisplacement recovery performance of the compressor is deteriorated,because the bleed passage has been closed thereby to prevent therefrigerant gas from being rapidly drawn from the crank chamber.

The present invention, which has been made in light of the aboveproblems, is directed to a swash plate type variable displacementcompressor which ensures the performance to recover displacement of thecompressor during the operation at a low rotational speed and to reducepower loss during the operation at a high rotational speed.

SUMMARY OF THE INVENTION

In accordance with an aspect of the present inventions a swash platetype variable displacement compressor includes a housing including acylinder block having a cylinder bore formed therein, a crank chamberformed in the housing, a rotary shaft extending through the crankchamber, and a swash plate connected to the rotary shaft. The rotaryshaft is rotatably supported by the housing. The swash plate isintegrally rotatable with the rotary shaft and inclinable relative tothe rotary shaft. The compressor further includes a piston received inthe cylinder bore to be reciprocally movable, a discharge pressureregion for receiving discharge pressure gas, a suction pressure regionfor receiving, suction pressure gas, a supply passage connecting thecrank chamber to the discharge pressure region and first and secondbleed passages. The supply passage is provided with a displacementcontrol valve. The pressure in the crank chamber is varied by adjustingthe opening of the displacement control valve to change the inclinationangle of the swash plate thereby to control the displacement of thecompressor. The first bleed passage connecting the crank chamber to thesuction pressure region is provided with a valve and the second bleedpassage constantly connecting the crank chamber to the suction pressureregion is provided with a throttle. The valve operates to close thefirst bleed passage according to the magnitude of centrifugal forcegenerated by the rotation of the rotary shaft.

Other aspects and advantages of the invention will become apparent fromthe following description, taken in conjunction with the accompanyingdrawings, illustrating by way of example the principles of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention that are believed to be novel areset forth with particularity in the appended claims. The inventiontogether with objects and advantages thereof, may best be understood byreference to the following description of the presently preferredembodiments together with the accompanying drawings in which:

FIG. 1 is a longitudinal cross-sectional view of a swash plate typevariable displacement compressor according to a first preferredembodiment of the present invention;

FIG. 2 is an enlarged cross-sectional view of a valve used in thecompressor according to the first preferred embodiment of the presentinvention;

FIG. 3 is an enlarged fragmentary cross-sectional view of the compressoraccording to the first preferred embodiment of the present invention;

FIG. 4 is a schematic block diagram illustrating the compressoraccording to the first preferred embodiment of the present invention;

FIG. 5 is a schematic graph showing a relation between the rotationalspeed of a rotary shaft of the compressor and the total cross-sectionalarea of throttle opening in bleed passages of the compressor accordingto the first preferred embodiment of the present invention;

FIG. 6 is an enlarged fragmentary cross-sectional view of the compressorshowing the valve according to a second preferred embodiment of thepresent invention;

FIG. 7 is an enlarged fragmentary cross-sectional view of the compressorshowing the valve according to a third preferred embodiment of thepresent invention, and

FIG. 8 is a schematic view as seen in the direction of the arrow D inFIG. 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following will describe a swash plate type variable displacementcompressor (hereinafter referred to as “compressor”) according to thefirst preferred embodiment of the present invention with reference toFIGS. 1 through 5. Referring to FIG. 1, the compressor designated bynumeral 10 has a housing 11 forming the outer shell of the compressor10. The housing 11 includes a cylinder block 12, a front housing 13joined to the front end of the cylinder block 12, and a rear housing 14joined to the rear end of the cylinder block 12. The cylinder block 12has a plurality of cylinder bores 12A formed therein. In FIG. 1, theleft side of the drawing corresponds to the front side of the compressor10, and the right side of the drawing corresponds to the rear side ofthe compressor 10. The front housing 13, the cylinder block 12 and therear housing 14 are fastened together in the longitudinal direction ofthe compressor 10 by a plurality of bolts 15 (only one bolt being shown)inserted through the front housing 13, the cylinder block 12 and therear housing 14, thus the housing 11 of the compressor 10 is formedthereby.

The front housing 13 has a crank chamber 16 formed therein, whose rearend is closed by the cylinder block 12. A rotary shaft 17 extendsthrough the center of the crank chamber 16 and is rotatably supported bythe front housing 13 and the cylinder block 12 through radial bearings18, 19, respectively. A shaft seal mechanism 20 is disposed in slidecontact with the circumferential surface of the rotary shaft 17 at aposition forward of the radial bearing 18 supporting the front part ofthe rotary shaft 17. The seal mechanism 20 has a lip seal member toprevent refrigerant gas in the crank chamber 16 from leaking out throughthe clearance between the front housing 13 and the rotary shaft 17. Therotary shaft 17 is connected at the front end thereof to an externaldrive source (not shown) through a power transmission mechanism (notshown either) so as to be rotated by the external drive source.

A lug plate 21 is fixedly mounted on the rotary shaft 17 in the crankchamber 16 so as to rotate integrally therewith. A swash plate 23 as apart of displacement changing mechanism 22 of the compressor 10 isprovided on the rotary shaft 17 behind the lug plate 21 and supported insuch a way that it is slidable in the axial direction of the rotaryshaft 17 and inclinable relative to the axis of the rotary shaft 17. Ahinge mechanism 24 is interposed between the swash plate 23 and the lugplate 21, through which the swash plate 23 and the lug plate 21 areconnected such that the swash plate 23 is integrally rotatable with thelug plate 21 and the rotary shaft 17, while inclinable relative to therotary shaft 17.

A coil spring 25 is disposed on the rotary shaft 17 between the lugplate 21 and the swash plate 23. A sleeve 26 is slidably disposed on therotary shaft 17 and urged rearward by the pressing force of the coilspring 25. The swash plate 23 is urged by the coil spring 25 through thesleeve 26 rearward or in the direction that decreases the inclinationangle of the swash plate 23. The inclination angle of the swash plate 23means an angle between the swash plate 23 and an imaginary plane that isperpendicular to the axis of the rotary shaft 17. The swash plate 23 hasa restricting portion 23A projecting from the front end thereof andabutable with the lug plate 21′, thereby restricting the maximuminclination angle of the swash plate 23. The rotary shaft 17 has a snapring 27 fitted thereon behind the swash plate 23. The rear end of theswash plate 23 is abutable with the snap ring 27, thereby restrictingthe minimum inclination angle of the swash plate 23. Referring to FIG.1, the swash plate 23 indicated by the solid line represents theposition at the maximum inclination angle thereof, and the swash plate23 indicated by the double-dashed line represents the position at theminimum inclination angle thereof.

Each cylinder bore 12A of the cylinder block 12 receives therein areciprocally movable single-headed piston 29. The piston 29 engages atthe neck portion thereof with the outer periphery of the swash plate 23′through a pair of shoes 30. As the swash plate 23 is rotated with therotary shaft 17, each piston 29 is reciprocated in its associatedcylinder bore 12A through the pair of shoes 30.

As shown in FIG. 1, the front end of the rear housing 14 is joined tothe rear end of the cylinder block 12 through a valve plate 32. The rearhousing 14 has a suction chamber 38 which serves as a suction pressureregion formed at a center region thereof. The suction chamber 38 is incommunication with a compression chamber 31 defined by the cylinder bore12A through a suction port 36 formed through the valve plate 32. Therear housing 14 also has a discharge chamber 39 which serves as adischarge pressure region formed at a circumferential region thereof.The discharge chamber 39 and the suction chamber 38 are separated by apartition wall 14A. The valve plate 32 defining the compression chamber31 with the piston 29 in the cylinder bore 12A has a discharge port 37formed therethrough in communication with the discharge chamber 39. Thesuction port 36 and the discharge port 37 for each cylinder bore 12A areprovided with a suction valve 33 and a discharge valve 34, respectively.

When the piston 29 moves toward the bottom dead center from the top deadcenter thereof, refrigerant gas in the suction chamber 38 is drawn intothe compression chamber 31 through the suction port 36 and the suctionvalve 33. Refrigerant gas drawn into the compression chamber 31 iscompressed to a predetermined pressure by the motion of the piston 29from the bottom dead center to the top dead center thereof, anddischarged into the discharge chamber 39 through the discharge port 37and the discharge valve 34.

A supply passage 42 is formed in the cylinder block 12 and the rearhousing 14 to connect the discharge chamber 39 to the crank chamber 16.An electromagnetic displacement control valve 35 is disposed in thesupply passage 42. The displacement control valve 35 is in communicationwith the suction chamber 38 through a pressure sensing passage 61. Theopening of the displacement control valve 35 is adjustable according tothe detected pressure in the suction chamber 38 or in response to anyexternal command signals. Adjusting the opening of the displacementcontrol valve 35 varies the flow rate of high-pressure refrigerant gasintroduced from the discharge chamber 39 into the crank chamber 16. Thepressure differential between the crank chamber 16 and the compressionchamber 31 across the piston 29 is varied, thereby changing theinclination angle of the swash plate 23. Accordingly, the stroke lengthof the piston 29 is varied thereby to control the displacement of thecompressor 10.

The center of the cylinder block 12 has a shaft hole 43 therethrough,and a recess 44 located behind and in communication with the shaft hole43. The rear end of the rotary shaft 17 is inserted into and supportedby the shaft hole 43 through the radial bearing 19. The compressor 10 ofthe first preferred embodiment includes a first bleed passage 48 and asecond bleed passage 58. A passage hole 45 forming a part of the firstbleed passage 48 extends in the rotary shaft 17 along its center axis.The front end portion of the passage hole 45 is opened to the crankchamber 16 at a position adjacent to the radial bearing 18 and the shaftseal mechanism 20. The passage hole 45 is closed at the rear end by aplug 60. A valve 50 is mounted on the rotary shaft 17 at the rear endportion thereof in the recess 44. The valve 50 will be described indetail later.

A thrust bearing 46 and a support spring 47 are interposed between therear end of the rotary shaft 17 and the valve plate 32. The recess 44 isin communication with the suction chamber 38 through a communicationhole 49 formed at the center of the valve plate 32. The communicationhole 49 serves as a throttle for restricting flow rate of refrigerantgas drawn from the crank chamber 16 into the suction chamber 38. Theaforementioned first bleed passage 48 includes the passage hole 45, therecess 44, the valve 50 and the communication hole 49 so as to connectthe crank chamber 16 to the suction chamber 38.

The valve 50 is provided for opening or closing the first bleed passage48. As shown in FIG. 2, the rotary shaft 17 has plane seating surfaces51, 52 formed by cutting off the top and bottom of the circumferentialsurface of the rear end portion of the rotary shaft 17, respectively. Avalve hole 53 is formed in the radial direction of the rotary shaft 17,or the compressor 10 so as to provide fluid communication between theseating surfaces 51′, 52 and also to be in communication with thepassage hole 45. The valve hole 53 is larger in diameter on the sideopened to the seating surface 51 than the opposite side opened to theseating surface 52. A valve body 54 is movably mounted on the rotaryshaft 17 so as to open or close the valve hole 53. The valve body 54 isdisposed on the side of the seating surface 51, and a counterweight 55connected to the valve body 54 through a connecting portion 56 isdisposed on the side of the seating surface 52. A coil spring 57 servingas an urging member is provided-between the seating surface 51 and thevalve body 54 for urging the valve body 54 toward its opened position.

A centrifugal force acting on the counterweight 55 is increased with anincrease in rotational speed of the rotary shaft 17, with the resultthat the counterweight 55 is moved away from the axis of the rotaryshaft 17. Accordingly, the valve body 54 is moved toward the axis of therotary shaft 17 against the urging force of the coil spring 57 andbrought into contact with the seating surface 51, thereby to close thevalve hole 53. On the other hand, the centrifugal force acting on thecounterweight 55 is decreased with a decrease in rotational speed of therotary shaft 17, with the result that the urging force of the coilspring 57 becomes greater than the centrifugal force acting on thecounterweight 55. Accordingly, the valve body 54 is moved away from theaxis of the rotary shaft 17 by the urging force of the coil spring 57,thereby to open the valve hole 53. FIGS. 1 and 2 show the valve 50 inits opened position during compressor operation at a high rotationalspeed of the rotary shaft 17, and FIG. 3 shows the valve 50 in itsclosed position during compressor operation at a low rotational speed ofthe rotary shaft 17.

Referring back to FIG. 1, the second bleed passage 58 connecting thecrank chamber 16 to the suction chamber 38 is formed in the cylinderblock 12. The second bleed passage 58 has a throttle hole 59 formed inthe valve plate 32 which functions as a fixed throttle for throttlingthe flow rate of the refrigerant gas. The crank chamber 16 is inconstant communication with the suction chamber 38 through the secondbleed passage 58.

Referring to FIG. 4 showing a schematic block diagram illustrating thecompressor 10 according to the first preferred embodiment, the dischargechamber 39 is in communication with the crank chamber 16 through thesupply passage 42 in which the displacement control valve 35 isdisposed. The crank chamber 16 is in communication with the suctionchamber 38 through the first bleed passage 48 and the second bleedpassage 58. The first bleed passage 48 is provided with the valve 50operable to open or close according to the magnitude of the centrifugalforce and the second bleed passage 58 is provided with the throttle hole59 serving as a fixed throttle.

FIG. 5 is a schematic graph showing a relation between rotational speedN of the rotary shaft 17 of the compressor 10 and total cross-sectionalarea AS of the throttle opening which is the sum of the cross-sectionalareas of the throttle openings formed in the first and second bleedpassages 48, 58 according to the first preferred embodiment. In thegraph of FIG. 5, the cross-sectional areas of the communication hole 49provided in the first bleed passage 48 and the throttle hole 59 providedin the second bleed passage 58 are designated by reference symbols AA,AB, respectively. During the operation of the compressor 10 at a lowrotational speed, the valve 50 is in its opened position. In this state,the relation among total cross-sectional area AS1 of the throttleopening, the cross-sectional area AA of the communication hole 49 andthe cross-sectional area AB of the throttle hole 59 is expressed byAS1=AA+AB. On the other hand, during the operation of the compressor 10at a high rotational speed, the valve 50 is in its closed position, thatis, the first bleed passage 48 is closed and only the second bleedpassage 58 is opened. When the rotational speed of the rotary shaft 17is at or higher than NC1, the relation among total cross-sectional areaAS2 of the throttle opening, the cross-sectional area AA of thecommunication hole 49 and the cross-sectional area AB of the throttlehole 59 is expressed by AS2=AB. The flow rate of refrigerant, gas drawnfrom the crank chamber 16 into the suction chamber 38 through the firstand second bleed passages 48, 58 is proportional to the totalcross-sectional area AS of the throttle opening. Therefore, the flowrate of refrigerant gas during the operation at a low rotational speedthat is expressed by AS1 (=AA+AB) is larger than that during theoperation at a high rotational speed that is expressed by AS2 (=AB). Thecross-sectional areas AA and AB are previously set at any valuessuitable to ensure both of the displacement recovery and power lossreduction during the operation of the compressor 10. The diameter of thefully opened valve hole 53 is set such that the cross-sectional area ofsuch valve hole 53 is larger than the cross-sectional area AA of thecommunication hole 49.

The following will describe the operation of the compressor constructedas described above. As the rotary shaft 17 is rotated by the externaldrive source such as a vehicle engine, the swash plate 23 is rotatedwith the rotary shaft 17 through the lug plate 21 and the hingemechanism 24. Accordingly, the rotational movement of the swash plate 23is converted into reciprocating movement of the piston 29 by way of theshoes 30. The piston 29 is reciprocated in the cylinder bore 12A,thereby causing refrigerant gas to be drawn from the suction chamber 38into the compression chamber 31 through the suction port 36 and thesuction valve 33. Then the refrigerant gas is compressed in thecompression chamber 31 to a predetermined pressure and discharged intothe discharge chamber 39 through the discharge port 37 and the dischargevalve 34. Most of the high-pressure refrigerant gas discharged into thedischarge chamber 39 is delivered to the external refrigeration circuit(not shown), while a part of the high-pressure refrigerant gas in thedischarge chamber 39 is drawn into the crank chamber 16 through thesupply passage 42 for varying the inclination of the swash plate 23.

The opening of the displacement control valve 35 provided in the supplypassage 42 is adjusted to control the relation between the flow rate ofrefrigerant gas introduced from the discharge chamber 39 into the crankchamber 16 and the flow rate of refrigerant gas flowing out from thecrank chamber 16 into the suction chamber 38 through the first andsecond bleed passages 48, 58. A crank chamber pressure PC in the crankchamber 16 is determined by this relation of the refrigerant gas. As theopening of the displacement control valve 35 is adjusted to change thecrank chamber pressure PC in the crank chamber 16, the pressuredifferential between the crank chamber 16 and the compression chambers31 through the piston 29 varies thereby to change the inclination angleof the swash plate 23. Thus; the stroke length of the piston 29 ischanged and the displacement of the compressor 10 is changedaccordingly.

When the cooling load is large due to high temperature in the vehiclecompartment, a suction pressure PS in the suction chamber 38 is high andthere is substantially no pressure differential between the pressures inthe compression chambers 31 and the crank chamber pressure PC in thecrank chamber 16 through the piston 29. (or PS≈PC). In this case, thedisplacement control valve 35 is controlled to be closed so that thesupply passage 42 prevents high-pressure refrigerant gas in thedischarge chamber 39 from flowing into the crank chamber 16. Since thecrank chamber pressure PC in the crank chamber 16 is substantially thesame as the suction pressure PS, refrigerant gas does not flow from thecrank chamber 16 through the first and second bleed passages 48, 58 intothe suction chamber 38. Thus, as Indicated by the solid line in FIG. 1,the swash plate 23 is moved to its maximum inclination angle position toincrease the stroke of the piston 29, thereby to increase thedisplacement of the compressor 10. During the maximum displacementoperation of the compressor 10, the refrigerant gas does not circulatethrough the supply passage 42, the first and second bleed passages 48,58, with the result that the compressor 10 is efficiently operated.

When the cooling load is decreased due to a decrease of the temperaturein the vehicle compartment, the suction pressure PS in the suctionchamber 38 is also decreased. In this case, the displacement controlvalve 35 is controlled to be opened in accordance with the decrease inthe suction pressure PS. Accordingly high-pressure refrigerant gas inthe discharge chamber 39 is introduced into the crank chamber 16 throughthe supply passage 42. As a result, the crank chamber pressure PC in thecrank chamber 16 is increased and the pressure differential between thecrank chamber 16 and the compression chambers 31 through the piston 29increases. The inclination angle of the swash plate 23 becomes small inaccordance with the increase of the pressure differential, therebydecreasing the displacement of the compressor 10.

During the variable displacement operation of the compressor 10, inparticular, when the rotational speed of the rotary shaft 17 is low, thecentrifugal force generated by the rotation of the rotary shaft 17 issmall. In this case, the valve body 54 of the valve 50 provided in thefirst bleed passage 48 is positioned so as to open the valve hole 53, asshown in FIG. 2. The second bleed passage 58 has the throttle hole 59for constant communication between the crank chamber 16 and the suctionchamber 38. That is, the first bleed passage 48 provided with the valve50 and the second bleed passage 58 provided with the throttle hole 59are opened. Thus, the refrigerant gas is drawn from the crank chamber 16into the suction chamber 38 rapidly and, therefore, the displacement ofthe compressor 10 is controlled appropriately in accordance with achange in the cooling load.

As the rotational speed of the rotary shaft 17 is increased, thecentrifugal force generated by the rotation of the rotary shaft 17 isincreased. That is, the centrifugal force acting on the counterweight 55of the valve 50 is also increased. As shown in FIG. 3, the valve body 54is moved toward the axis of the rotary shaft 17 by the centrifugal forceacting against the urging force of the coil spring 57 so as to bebrought into contact with the seating surface 51, thereby to close thevalve hole 53. The first bleed passage 48 provided with the valve 50 isclosed and only the second bleed passage 58 provided with the throttlehole 59 is opened. Thus, the flow rate of refrigerant gas drawn from thecrank chamber 16 into the suction chamber 38 is decreased. The decreaseof the flow rate of refrigerant gas circulating within the compressormeans the increase the flow rate of refrigerant gas in the externalrefrigeration circuit, thus reducing the power loss of the compressor10.

As the cooling load is decreased to be nearly zero due to furtherdecrease of the temperature in the vehicle compartment, the suctionpressure PS in the suction chamber 38 is further decreased accordinglyand the displacement control valve 35 becomes fully opened. In thiscase, a large amount of high-pressure refrigerant gas is introduced fromthe discharge chamber 39 into the crank chamber 16 through the supplypassage 42, thereby to increase the crank chamber pressure PC in thecrank chamber 16. As a result, the pressure differential between thecrank chamber 16 and the compression chamber 31 through the piston 29 isincreased. As indicated by the double-dashed line in FIG. 1, the swashplate 23 is moved to its minimum inclination angle position to decreasethe stroke length of the piston 29, thereby to change the displacementof the compressor 10 to the minimum. During the minimum displacementoperation (or OFF operation), the displacement of the compressor 10 isnot zero. When the compressor 10 is operated at a high rotational speedduring the minimum displacement operation, the flow rate of refrigerantgas circulating within the compressor 10 is further decreased thereby todecrease the level of the minimum displacement. Thus, the power lossduring the minimum displacement operation is reduced.

The following will describe the recovery of the compressor 10 from theminimum displacement state. The increase of the displacement of thecompressor 10 from the OFF operation is dependent on the rate ofrefrigerant gas from the crank chamber 16 into the suction chamber 38.When the rotary shaft 17 is rotated at a low speed, the first bleedpassage 48 provided with the valve 50 and the second bleed passage 58provided with the throttle hole 59 are both opened. Therefore, therefrigerant gas is drawn from the crank chamber 16 into the suctionchamber 38 rapidly and the crank chamber pressure PC in the crankchamber 16 is decreased accordingly rapidly. Thus, the recovery of thecompressor 10 from the minimum displacement state is improved.

When the rotary shaft 17 is rotated at a high speed, the first bleedpassage 48 provided with the valve 50 is closed and only the secondbleed passage 58 provided with the throttle hole 59 is opened.Accordingly, the flow rate of refrigerant gas drawn from the crankchamber 16 into the suction chamber 38 is decreased. During thehigh-speed operation of the compressor 10, however, an inertial forceacting on the piston 29′ and the swash plate 23 is increased so as toprincipally affect the motion of the piston 29 and the swash plate 23 tochange in the direction that increases the compression displacement.Thus, the desired compression displacement is achieved rapidly from theminimum displacement state despite the decrease of the flow rate ofrefrigerant gas drawn from the crank chamber 16 into the suction chamber38.

The swash plate type variable displacement compressors 10 according tothe first preferred embodiment of the present invention offers thefollowing advantageous effects.

(1) When the rotational speed of the rotary shaft 17 is low and,therefore, the centrifugal force generated by the rotation of the rotaryshaft 17 is small, the valve body 54 of the valve 50 provided in thefirst bleed passage 48 is positioned so as to open the valve hole 53.The second bleed passage 58 has the throttle hole 59 providing constantcommunication between the crank chamber 16 and the suction chamber 38.That is, the first bleed passage 48 provided with the valve 50 and thesecond bleed passage 58 provided with the throttle hole 59 are bothopened. Thus, the refrigerant gas is drawn from the crank chamber 16into the suction chamber 38 rapidly and the crank chamber pressure PC isdecreased accordingly rapidly, thereby improving the recovery of thecompressor 10 from the minimum displacement state.(2) During the variable displacement operation of the compressor 10, thecentrifugal force generated by the rotation of the rotary shaft 17 andacting on the counterweight 55 of the valve 50 is increased with anincrease in the rotational speed of the rotary shaft 17. The valve body54 is moved toward the axis of the rotary shaft 17 by the centrifugalforce acting against the urging force of the coil spring 57 so as to bein contact with the seating surface 51, with the result that the valvehole 53 is closed. Since the first bleed passage 48 provided with thevalve 50 is closed and only the second bleed passage 58 provided withthe throttle hole 59 is opened, the flow rate of the refrigerant gasdrawn from the crank chamber 16 into the suction chamber 38 isdecreased. Such decreased flow rate of refrigerant gas within thecompressor 10 contributes to increasing the flow rate of refrigerant gasin the external refrigeration circuit, thereby to reduce the power lossand improve the operating efficiency of the compressor 10.(3) During the operation of the compressor 10 at a high rotationalspeed, the first bleed passage 48 provided with the valve 50 is closedand only the second bleed passage 58 provided with the throttle hole 59is opened. Thus, the refrigerant gas drawn from the crank chamber 16into the suction chamber 38 is decreased. In particular, during the OFFoperation, the minimum displacement of the compressor is furtherdecreased thereby to reduce the power loss. When the compressor 10 isoperated at a high rotational speed, the inertial force acting on thepiston 29 and the swash plate 23 is increased so as to affect theincrease of the compression displacement. Thus, the decrease of theperformance of the compressor 10 to recover the displacement of thecompressor 10 from the minimum displacement state is prevented despitethe decrease of the flow rate of refrigerant gas drawn from the crankchamber 16 into the suction chamber 38.(4) The valve 50 provided in the first bleed passage 48 formed in therotary shaft 17 is operable to be opened or closed by utilizing thecentrifugal force generated by the rotation of the rotary shaft 17.Further, the throttle hole 59 is easily provided in the second bleedpassage 58 formed in the cylinder block 12 separately from the firstbleed passage 48 to ensure a constant flow of refrigerant gastherethrough.(5) The passage hole 45 formed in the rotary shaft 17 along its axis isopened at one end thereof to the crank chamber 16 and has at the otherend thereof the valve 50, which allows the valve 50 to be disposedeffectively in the cylinder block 12.(6) The valve 550 includes the valve body 54, the coil spring 57 and thecounterweight 55. The coil spring 57 urges the valve body 54 toward itsopened position. The centrifugal force generated by the rotation of therotary shaft 17 and acting on the counterweight 55 causes the valve body54 to be moved against the urging force of the coil spring 57 and toclose the valve hole 53. When the rotational speed of the rotary shaft17 is increased, the counterweight 55 is moved away from the axis of therotary shaft 17 by the increasing centrifugal force acting on thecounterweight 55 against the urging force of the coil spring 57. As aresult, the valve body 54 is moved toward its closed position. On theother hand, when the rotational speed of the rotary shaft 17 isdecreased, the urging force of the coil spring 57 becomes greater thanthe centrifugal force acting on the counterweight 55, so that the valvebody 54 is moved to and held at its opened position. The valve 50 issimple in structure as described above and the first bleed-passage 48 isopened or closed reliably in accordance with the rotational speed of therotary shaft 17.

The following will describe a swash plate type variable displacementcompressor according to the second preferred embodiment of the presentinvention with reference to FIG. 6. The compressor of the secondpreferred embodiment differs from that of the first preferred embodimentin that the rotary shaft 17 is equipped with the function of the secondbleed passage 58 of the first embodiment. That is, the second bleedpassage of the second embodiment shares a part of the first bleedpassage. The rest of the structure of the compressor according to thesecond preferred embodiment is substantially the same as that of thefirst preferred embodiment. For the sake of convenience of explanation,therefore, like or same parts or elements will be referred to by thesame reference numerals as those that have been used in the firstpreferred embodiment, and the description thereof will be omitted.

As shown in FIG. 6, the rotary shaft 17 of the compressor 10 accordingto the second preferred embodiment has a throttle hole 70 radially boredtherethrough at a position adjacent to the valve 50 for providing fluidcommunication between the passage hole 45 in the rotary shaft 17 and therecess 44 in the cylinder-block 12. The throttle hole 70 functions as afixed throttle. The diameter D1 of the throttle hole 70 is formedsmaller than the diameter D2 of the communication hole 49 (or D1<D2). Asthe previously described first preferred embodiment, the relation amongthe cross-sectional area AA of the communication hole 49, thecross-sectional area AB of the throttle hole 59 and the totalcross-sectional area AS1 during the operation at a low rotational speedis expressed by AS1=AA+AB, while the total cross-sectional area AS2during the operation at a high rotational speed is expressed by AS2=AB.Meanwhile, in the second preferred embodiment, the diameter D1 of thethrottle hole 70 and the diameter D2 of the communication hole 49 areset such that D1=AB=AS2 and D2=AA+AB=AS1 respectively.

When the rotational speed of the rotary shaft 17 is low, the centrifugalforce generated by the rotation of the rotary shaft 17 is small, so thatthe valve body 54 of the valve 50 provided in the first bleed passage 48is positioned so-as to open the valve hole 53. The rotary shaft 17 hasthe throttle hole 70 for providing constant communication between thecrank chamber 16 and the suction chamber 38. In this case, the flow rateof the refrigerant gas drawn from the crank chamber 16 into the suctionchamber 38 depends on the diameter D2 of the communication hole 49. Asdescribed above, the diameter D1 of the throttle hole 70 is smaller thanthe diameter D2 of the communication hole 49 (or D1<D2). Therefore, therefrigerant gas in the crank chamber 16 is drawn rapidly into thesuction chamber 38 trough the recess 44 and the crank chamber pressurePC in the crank chamber 16 is decreased accordingly rapidly, with theresult that the performance of the compressor 10 to recover thedisplacement of the compressor 10 from the minimum displacement state isimproved.

During high-speed operation of the compressor 10, the centrifugal forcegenerated by the rotation of the rotary shaft 17 acting on thecounterweight 55 is increased and the valve body 54 is moved-toward theaxis of the rotary shaft 17 against the urging force of the coil spring57 until it is brought into contact with the seating surface 51, therebyto close the valve hole 53. Thus, the first bleed passage 48 providedwith the valve 50 is closed and only the throttle hole 70 is opened.Accordingly, the flow rate of refrigerant gas drawn from the crankchamber 16 into the suction chamber 38, which depends on the diameter D1of the throttle hole 70, is decreased. However, during the operation ofthe compressor 10 at a high rotational speed, the inertial force actingon the piston 29 and the swash plate 23 is increased so as toprincipally affect the motion of the piston 29 and the swash plate 23 tochange in the direction that increases the compression displacement.Thus, the desired compression displacement is achieved rapidly from theminimum displacement state despite the decrease of the flow rate ofrefrigerant gas drawn from the crank chamber 16 into the suction chamber38. In addition, the decreased flow rate of refrigerant gas circulatingwithin the compressor 10 during its variable displacement operationmeans the increase of the flow rate of refrigerant gas in the externalrefrigeration circuit, thereby to reduce the power loss. During the OFFoperation, the level of the minimum displacement of the compressor isfurther decreased. Thus, the power loss during the minimum displacementoperation is also reduced. FIG. 6 shows the valve 50 in its closedposition.

In the compressor 10 of the second preferred embodiment, the first bleedpassage 48 and the throttle hole 70 are both provided in the rotaryshaft 17. This structure contributes to reduction in production time andcost as compared with a structure wherein the first bleed passage 48 andthe throttle hole 70 are provided separately.

The following will describe a swash plate type variable displacementcompressor according to the third preferred embodiment of the presentinvention with reference to FIGS. 7 and 8. The compressor 10 of thethird preferred embodiment differs from that of the second preferredembodiment in that a groove 80 corresponding to the throttle hole 70 ofthe second preferred embodiment is formed in the valve hole 53 of thevalve 50. The rest of the structure of the compressor 10 according tothe third preferred embodiment is substantially the same as that of thesecond preferred embodiment. For the sake of convenience of explanation,therefore, like or same parts or elements will be referred to by thesame reference-numerals as those which have been used in the first andsecond preferred embodiments, and the description thereof will beomitted.

As shown in FIG. 7, in the compressor 10 according to the thirdpreferred embodiment, the groove 80 having a certain depth is formed atthe opening of the valve hole 53 of the valve 50 on the side of theseating surface 51. When the valve body 54 is in contact with theseating surface 51 by the centrifugal force, the valve body 54 and thegroove 80 cooperate to form a groove slit 81. The passage hole 45 iscommunicated with the recess 44 through the groove slit 81 whichfunctions as a throttle. The cross-sectional area of the groove slit 81when the valve body 54 is in contact with the seating surface 51 is setsmaller than that (D2) of the communication hole 49 and setsubstantially the same as that (D1) of the throttle hole 70 of thesecond preferred embodiment.

When the rotational speed of the rotary shaft 17 is low, the centrifugalforce generated by the rotation of the rotary shaft 17 is small and thevalve body 54 of the valve 50 provided in the first bleed passage 48 ispositioned to open the valve hole 53. In this case, since the grooveslit 81 is not formed, the flow rate of the refrigerant gas depends onthe diameter D2 of the communication hole 49. Refrigerant gas is drawnfrom the crank chamber 16 into the suction chamber 38 rapidly and thecrank chamber pressure PC in the crank chamber 16 is decreasedaccordingly rapidly. Thus, the recovery of the compressor 10 from theminimum displacement state is improved.

As the rotational speed of the rotary shaft 17 is increased, thecentrifugal force generated by the rotation of the rotary shaft 17 isincreased and the centrifugal force acting on the counterweight 55 ofthe valve 50 is also increased. The valve body 54 is then moved towardthe axis of the rotary shaft 17 by the centrifugal force against theurging force of the coil spring 57 until it is brought into contact withthe seating surface 51 thereby to close the valve hole 53. In this case,only the groove slit 81 whose diameter is smaller than that of thecommunication hole 49, is opened, so that the flow rate of therefrigerant gas drawn from the crank chamber 16 into the suction chamber38 is decreased. However, during the operation of the compressor 10 at ahigh rotational speed, the inertial force acting on the piston 29 andthe swash plate 23 is increased so as to principally affect the motionof the piston 29 and the swash plate 23 to change in the direction thatincreases the compression displacement. Thus, the desired compressiondisplacement is achieved rapidly from the minimum displacement statedespite the decrease of the flow rate of refrigerant gas drawn from thecrank chamber 16 into the suction chamber 38. In addition, the decreasedflow rate of refrigerant gas circulating within the compressor 10 duringits variable displacement operation means the increase of the flow rateof refrigerant gas in the external refrigeration circuit, therebyreducing the power loss. Further, during the OFF operation, thecompression displacement is decreased further than the minimumdisplacement. Thus, the power loss during the minimum displacementoperation is also reduced. FIG. 7 shows the valve 50 in its closedposition.

According to the third preferred embodiment, the groove 80 is merelyformed at the opening of the valve hole 53 of the valve 50. Thiscontributes to simplified structure and further reduction in theproduction time and cost of the compressor 10.

The present invention is not limited to the first through thirdpreferred embodiments, but it may be variously modified within the scopeof the invention. For example, the above embodiments may be modified asexemplified below.

In the second and third preferred embodiments, the throttle hole 70 orthe groove slit 81 is provided at one end of the rotary shaft 17 as athrottle. Alternatively, a fixed throttle may be formed through the plug60 closing rear end of the passage-hole 45 so that the passage hole 45and the recess 44 are in constant communication with each other.

In the third preferred embodiment, the groove 80 is provided on the sideof the seating surface 51 of the valve hole 53. Alternatively, thegroove 80 may be provided on the surface of the valve body 54. Further,the valve body 54 may have an elongated hole formed therein as athrottle providing fluid communication between the passage hole 45 andthe recess 44.

In the compressor 10 according to the first through third preferredembodiments any kind of refrigerant may be used, including preferablyfluorocarbon gas or carbon dioxide. Although the compressor 10 accordingto the foregoing embodiments have been described as a compressor forcompressing refrigerant gas, the present invention does not limit therefrigerant only to gaseous refrigerant.

Therefore, the present examples and embodiments are to be considered asillustrative and not restrictive, and the invention is not to be limitedto the details given herein but may be modified within the scope of theappended claims.

1. A swash plate type variable displacement compressor comprising: ahousing including a cylinder block having a cylinder bore formedtherein; a crank chamber formed in the housing; a rotary shaft extendingthrough the crank chamber, the rotary shaft being rotatably supported bythe housing; a swash plate connected to the rotary shaft, the swashplate being integrally rotatable with and inclinable relative to therotary shaft; a piston received in the cylinder bore to be reciprocallymovable; a discharge pressure region for receiving discharge pressuregas; a suction pressure region for receiving suction pressure gas; asupply passage connecting the crank chamber to the discharge pressureregion, the supply passage being provided with a displacement controlvalve, wherein the pressure in the crank chamber is varied by adjustingthe opening of the displacement control valve to change the inclinationangle of the swash plate thereby to control the displacement of thecompressor, and a first bleed passage connecting the crank chamber tothe suction pressure region, the first bleed passage being provided witha valve, a second bleed passage constantly connecting the crank chamberto the suction pressure region, the second bleed passage being providedwith a throttle, wherein the valve operates to close the first bleedpassage according to the magnitude of centrifugal force generated by therotation of the rotary shaft.
 2. The swash plate type variabledisplacement compressor according to claim 1, wherein the first bleedpassage includes a passage hole extending in the rotary shaft along thecenter axis, one end of the passage hole is opened to the crank chamber,the valve is disposed at the other end of the passage hole.
 3. The swashplate type variable displacement compressor according to claim 2,wherein the second bleed passage is formed separately from the firstbleed passage, wherein the throttle of the second bleed passage is afixed throttle.
 4. The swash plate type variable displacement compressoraccording to claim 2, wherein the second bleed passage shares at least apart of the first bleed passage.
 5. The swash plate type variabledisplacement compressor according to claim 4, wherein the throttle ofthe second bleed passage is a fixed throttle provided on the rotaryshaft.
 6. The swash plate type variable displacement compressoraccording to claim 4, wherein the valve has a valve body and a valveseat to contact with the valve body, the throttle of the second bleedpassage is a groove which is formed on the valve seat.
 7. The swashplate type variable displacement compressor according to claim 1,wherein the valve includes a valve body, an urging member urging thevalve body toward the opened position and a counterweight, wherein acentrifugal force generated by the rotation of the rotary shaft acts onthe counterweight to move the valve body toward the closed positionagainst the urging force of the urging member.
 8. The swash plate typevariable displacement compressor according to claim 6, wherein a valvehole is formed on the rotary shaft in the radial direction of the rotaryshaft, wherein the valve body of the valve is mounted on the rotaryshaft to open and close the valve hole.
 9. The swash plate type variabledisplacement compressor according to claim 7, wherein the urging memberis a coil spring.
 10. The swash plate type variable displacementcompressor according to claim 1, wherein the displacement control valveis an electromagnetic valve.